The present invention concerns a plastic spacer for insulating glass elements, wall panels or similar objects. Such spacers are used, for example, to keep the glass sheets in an insulating glass pane parallel to each other and, combined with sealant, seal the area formed between the glass sheets at its edges and contain desiccant.
Spacers are frequently employed in the form of hollow metal profiles (stainless steel or aluminium). The profile has two parallel side walls in contact with the glass sheets and two legs extending between the side walls, which essentially run at right angles to the side walls of the hollow profile and join these to each other.
As far as their bonding properties with conventional sealants and sealing against water vapour penetrating the area between the sheets from outside are concerned, they meet the requirements. Nevertheless, the heat flow at the sheet edges, depending on the metallic materials, is excessive. Even if the area between the sheets is filled with inert gases such as e.g. xenon or krypton, a serious loss in insulation quality is observed, particularly in the boundary area set into the window or facade frames.
Proposals to use plastic instead of metallic materials, as specified in DE-A-3302 659. DE-A-127 739, EP-A-0 430 889 and EP-A-0601 488 naturally produced an improvement in relation to heat insulation in the boundary area of the insulating glass element.
By doing this, however, serious problems characteristic of plastic result concerning:
the inadequate longitudinal stiffness and straightness of a plastic spacer compared with one produced from metallic material, which leads to considerably higher production cost and waste during manufacture; this problem can be countered to an extent by increasing the wall thicknesses of the profile. However, the result then is:
excessive heat transfer across the relatively large plastic wall thicknesses; and
increased production costs as a result of the higher material consumption.
The purpose of the present invention is to supply a common solution to the conflicting problems mentioned above using spacers made with a plastic base.
The invention purports to solve the problem in the spacers initially described by choosing the ratio of the thickness of the legs to the thickness of the side walls as 0.8 or less and/or the thermal resistance in the legs to be higher than that in the side walls.
Limiting the thickness ratio of the legs and side walls to 0.8 or less gives more freedom to improve longitudinal stiffness by increasing the wall thickness or the side wall thickness while simultaneously limiting the thickness of the legs to the dimensions required for transverse stability of the hollow profile, thus limiting heat transfer at right angles to the length of the profile from one side wall to the other to a minimum.
The choice of a higher thermal resistance in the legs provides reduced heat transfer at right angles to the length of the profile (in the leg level). As the legs form a limiting factor for heat transfer performance, it is now possible to plan and implement reinforcement of the plastic in the side walls with a view to improving longitudinal stiffness, in the main independent of heat transfer considerations. Therefore it is possible to use plastic/reinforcing material combinations, which must provide an optimum in relation to their joining properties, especially bonding between synthetic and reinforcing materials, together with improved mechanical properties, regardless of their influence on heat conducting capability.
The principle of construction of the spacer as specified in the invention makes the longitudinal stiffness required to handle hollow profiles during the production of insulating glass elements feasible due to the freedom to increase the thickness of the side walls, while still providing the advantage of reduced heat transfer associated with plastic and, moreover, the latter can be minimised due to the comparatively thin construction of the legs.
The side wall thickness of a hollow profile in a 20 mm wide spacer is e.g. 3 mm or less for preference.
The choice of wall thickness ratio and/or reinforcement of the plastic increases the longitudinal stiffness, preferably so that the profile in the level of the side walls bends at most by about 100 mm/m of profile length. This saves nugatory expenditure as the conventional devices in metallic spacers can be used.
In addition, the transverse stability required for the hollow profile is the principal determinant for the thickness of the legs, i.e. the capability of the profile to support and retain both glass sheets of the insulating glass element at a defined spacing, even if wind forces acting on the sheets product tensile and/or pressure loading.
Surprisingly, it became apparent at the same time that, as a result of the lower wall thickness of the legs, together with the elasticity properties inherent in plastic, the hollow profile acquires a capacity to adapt in the transverse direction, which allows it to match its cross section at least partially to distortion of the glass sheets (the effect of wind forces). In addition, the legs permit elastic elongation or compression in the transverse direction, so that the position of the side walls of the profile can at least partially follow the distortion or bending of the glass sheets.
This has the effect of lowering the demands on the sealing components placed between the spacer and the glass sheets considerably when the glass sheets are subjected to tension and pressure, which is not only good for the long term stability of the sealing components themselves, but also noticeably counteracts separation tendencies in the glass/sealing component and sealing component/spacer boundary areas.
Limiting the thickness ratio to about 0.6 or less, or even to 0.4 or less, provides a further decrease in heat transfer, thus achieving or simultaneously improving on the abovementioned additional benefits.
It is possible to reduce the thickness of the side walls and, above all, the legs, by arranging one or more links inside the cavity parallel to the side walls, and still maintain comparable longitudinal stiffness. It is possible to form these links extending, in the main, across the entire height of the hollow profile and, in this way, join both legs to each other. Alternatively, the links can also form ribs running along the profile, with an edge standing proud of a leg.
The plastic can be reinforced to minimise wall thickness further, while maintaining or even increasing rigidity, in particular the longitudinal stiffness as well.
In addition, the proportion of reinforcing material in the plastic of the side walls will be higher than that in the legs. This measure is particularly relevant considering that numerous preferred reinforcing materials have a higher specific thermal conductivity than the plastic itself. By reinforcing the plastic in the legs as well, it is possible to reduce their thickness further, though by doing this, in the light of the effect this has on the thermal conductivity of the hollow profile, it is not possible to increase the proportion of reinforcing material arbitrarily. With respect to the thermal conductivity of the plastic, it is beneficial to seek an optimum ratio between reinforcing materials and costs.
With regard to minimising the heat transfer properties of the legs, it is preferable to reinforce these only in part. In this connection, there is the option of reinforcing strip shaped areas running parallel to the profile length, maintaining separation from the side walls and the legs if these are present. This solution strengthens an area of the legs which is mechanically weaker and limits the heat transfer through the legs in another, by means of the non-reinforced areas of the legs adjoining the side walls and, if necessary, the links.
Reinforcing fibres are the first choice for reinforcing materials, preferably chosen from among glass fibres, carbon fibres, aramide fibres and/or natural fibres. These can be inset as short fibres, long fibres or, if necessary, continuous fibres, or any combination of these.
In addition to reinforcing fibres, and as an alternative if necessary, it is also possible to strengthen plastic with particle shaped materials, i.e. especially in granular or disc shape. In this connection, Wollastonite, mica and talc are particle shaped materials.
If reinforcing materials are set into the side walls and, as required, the links, for strengthening purposes, it is advantageous to incorporate these in the plastic, preferably oriented along the hollow profile.
If fibres are used to reinforce the legs, it is advantageous to arrange these crossing one another, as this produces a larger heat conduction path in the individual reinforcing fibres, i.e. the hollow profile has a lower heat transfer capacity.
It is advisable to use fibres, as required, in the form of linked material such as e.g. a fibre mat or net, to implement the criss-cross arrangement of the reinforcing fibres.
From the aspects discussed above, the proportion of reinforcing materials as a percentage by weight will be higher in the side walls than in the legs. This is equally applicable to links parallel to the side walls, possibly placed in the hollow profile cavity.
Sheet metal strips arranged parallel to the side walls are a particularly cost effective method of reinforcing the latter. These strips can be applied to the profile externally, in particular by bonding. It is, however, preferable to embody the sheet metal strips in the plastic of the side walls to avoid from the outset corrosion problems, bonding problems with sealing and bonding components or even handling problems with profiles produced initially without the sheet metal strips. Moreover, it is possible in this way to avoid the bonding process as a production stage.
It is advantageous to use perforated sheet metal strips, which permit a particularly good mechanical bond with the plastic of the side walls.
However, sheet metal strips provided additionally with indentations or surface irregularities produced in other ways have advantages which, nonetheless, do not produce quite the same mechanical bonding effect with the surrounding plastic as do perforated sheet metal strips, especially when they are incorporated in the side walls.
Despite the higher thermal conductivity of the metallic material from which sheet metal strips are made, these lead at best to an imperceptible increase in the heat transfer qualities of the hollow profile.
Typical sheet metal thicknesses are in the region of 0.1 to 1.0 mm, and, if the sheet metal strips are embedded in the side walls, it is preferable for the sheet metal thickness not to be greater than half the thickness of the side walls.
It is also possible to use sheet metal strips independently to reinforce links in a profile.
It is possible to achieve a further reduction in heat transfer through the profile with synthetic foam materials. Alternatively, either for this purpose or to complement it, it is possible to consider reinforcing materials/filling material such as e.g. hollow glass balls, hollow fibres etc., which contain a certain volume of gas.
It is beneficial if the spacer as specified in the invention has longitudinal and/or transverse grooves on the external surfaces of the side walls. In this connection, it is possible to improve bonding of the sealing components with the spacer.
It is possible to achieve a similar effect with the spacer as specified in the invention by providing retention agents, especially in the form of indentations, irregularities or undercuts for quasi-mechanical anchoring of the sealant for the side walls to its external surfaces. It is equally possible to do this with the external surfaces of the sheet metal strips if these are placed externally to reinforce the side walls.
The use of a protective layer, for example an epoxy layer or an inorganic/organic compound layer, which again provides other functions, namely bonding of the sealant and hollow profile, together with a certain degree of UV protection, is a critical step concerning the chemical resistance of plastic spacers. It avoids the need to use more expensive sealing components designed specifically for plastic. At the same time, such layers provide additional thermal insulation.
Whereas strict limits for spacer production are drawn concerning the selection of the plastics to be used as regards their chemical resistance to sealing and bonding component materials, such as e.g. butyl bonding components, polysulphide, polyurethane and silicone sealing components and their tendency to give off gas forming materials (fogging problems) and their diffusibility (vapour diffusion sealing)xe2x80x94 a very good plastic in this respect is Styrol-acrylonitrile-copolymerxe2x80x94 it is also possible to use a suitable layer of significantly cheaper plastic, such as e.g. PVC, polyacryl, polyester, polystyrol or polypropylene.
If suitably selected, the protective layer can also perform the function of a vapour diffusion barrier. Such a vapour barrier will be extremely advisable for many plastics, to avoid water vapour entering the space between the glass sheets and hence premature depletion of the desiccant in the hollow profile, which would result in condensation forming inside the insulating glass elements.
The recommended epoxy layer, in its function as a vapour barrier, has the advantage, compared with the metal foils conventionally recommended, of being more resistant to crack formation and detachments appearing than metal foils attached to or embodied in the profile. Moreover, this will avoid the problem associated with widely differing coefficients of thermal expansion (bimetallic effect).
The recommended protective layer specified in the invention can also improve chemical resistance to sealants so that is solves long observed tensile fracture corrosion problems.
The outer leg can be provided on the outside with a diffusion barrier in the form of thin aluminium foil, stainless steel foil, or plastic foil coated either with vaporised metal or inorganic/organic compounds.
This diffusion barrier can be attached directly to the plastic of the leg and, as required, enclosed in an epoxy layer. A further option is to introduce the metal foil to the plastic during the extrusion process.
It is also possible to imagine an epoxy layer placed between the diffusion barrier and the outer surface of the leg.
In the conventional manufacturing process for metallic spacers for insulating glass framing elements, pre-cut hollow profile extrusions are bent to form in the corners, with the inside legs under strain. If this technique is applied to plastic spacers, production problems which are difficult to resolve occur as a result of the elastic plastic returning to its original shape, such as e.g. unacceptable positioning and form deviations in the area of the corners. Moreover, even if the area to be bent is warmed, excessive distortions, delays, cracks and high production times occur. Existing diffusion barrier coatings in the area of the corners processed in this way may not remain undamaged and, frequently, may even be totally destroyed.
As, in addition, the bending area must be chosen to be relatively large due to the properties of plastics compared with metals, the interior of the hollow profile becomes significantly constricted which, on one hand, makes filling the profile cavity/cavities with desiccant very difficult and, on the other, leads to a decrease in the sealing surface area.
The production of polygon-shaped frames as specified in the invention, in which each corner of the hollow profile areas forming the frame is provided with a V-shaped opening, produced by removing the inner leg while leaving the outer leg essentially intact, the side walls tapering towards the corner, counters this. The contact areas or cut edges of the side walls of the V-shaped opening are folded inwards to form the frame.
Alternatively, the spacer, forming a polygon-shaped frame, in which the areas forming each corner of the frame of the hollow profile contain a V-shaped opening extending over the whole width of the outer leg and, essentially, over the entire height of the side walls, in which the vertex of the V-shaped opening is in the inner leg can have a triangular cap placed on the opened out legs to form the corner.
In both alternatives, the contact joints to be produced in the area of the corners are to be firmly joined to one other, preferably by means of butt, laser, ultra-sound or high frequency welding or bonding.